Conventionally, for an insulated covering material for an insulated wire used in carrying out wiring of parts for a car such as an automobile, electric/electronic equipment and the like, generally in wide use is a vinyl chloride resin excellent in flame retardancy, into which, according to a variety of required properties including mechanical properties such as wear resistance, tensile strength and tensile elongation, flexibility, and workability, additives such as a plasticizer and a stabilizer are blended as appropriate and adjustments are made to types and blending amounts of the additives.
However, there is a problem that the vinyl chloride resin, having flame retardancy by itself, includes halogen elements in its molecular chains, so that it emits harmful halogenous gas into the atmosphere in case of car fire or at the time of combustion for disposing of electric/electronic equipment by incineration, causing environmental pollution.
Under the circumstances, developed these days has been a so-called non-halogenous flame-retardant resin composition, which is prepared by using polyethylene, polypropylene or the like as its base resin and adding a metallic hydrate such as magnesium hydroxide as a flame retardant; however, there is a disadvantage that mechanical properties such as wear resistance remarkably degrade since the non-halogenous flame-retardant resin composition requires a large amount of metallic hydrate to be added thereto as the flame retardant.
Thus, in order to overcome such a disadvantage, for example, Japanese Patent Gazette No. 3280099 discloses an art of using a plurality of polyolefin resins and rubbers as the base resin, in which a specific functional group is further contained by a specific amount so as to increase an affinity between the base resin and the metallic hydrate and improve mechanical properties such as wear resistance.
However, the following problems arise when the conventionally-known non-halogenous flame-retardant resin composition, especially, a non-crosslinked flame-retardant resin composition is used as the insulated covering material for the insulated wire. Specifically, when the insulated covering material is used in areas exposed to high temperature environment such as an engine room in an automobile, there arises a problem that the insulated covering material is unintentionally molten.
In addition, as the insulated covering material for the insulated wire used in areas requiring high heat resistance is generally subjected to crosslinking such as electron irradiation crosslinking and silane crosslinking, there arises a problem that the cost of manufacturing is increased if dedicated equipment is employed in such crosslinking.
Besides, in the case of using the insulated wire in an automobile and the like, it is generally often the case that a plurality of insulated wires are tied into a wire bundle, around which a protective material in various shapes such as a tape, tube or sheet is wound to be utilized as a wiring harness.
At this time, as the insulated wires making up the wiring harness, not only non-halogenous insulated wires in which non-halogenous flame-retardant resin compositions are used as insulated covering materials are used, but also vinyl chloride insulated wires and the like in which vinyl chloride resin compositions such as polyvinyl chloride are used as insulated covering materials are abundantly used, empirically.
Therefore, mixed use of the non-halogenous insulated wires and the vinyl chloride insulated wires is difficult to completely avoid. Under these circumstances, it turned out that if the non-halogenous insulated wires are used in contact with the vinyl chloride insulated wires and the like, there arises a problem of remarkably deteriorating the insulated covering material for the non-halogenous insulated wires in the wire bundle to degrade heat resistance.
Further, since the vinyl chloride resin composition and the like are usually used as a base material for the wiring-harness protective material wound around the wire bundle, it turned out that the same problem arises if the non-halogenous insulated wire is used in contact with a vinyl-chloride wiring-harness protective material and the like.
Though a detailed mechanism of the sources of the problems is not found yet, those problems are assumed to arise because an antioxidant in the insulated covering material composed of the non-halogenous flame-retardant resin composition is remarkably consumed, or the antioxidant itself makes a transition into the vinyl chloride insulated wire or the vinyl-chloride wiring-harness protective material when the vinyl chloride insulated wire, the vinyl-chloride wiring-harness protective material or the like comes into contact with the non-halogenous insulated wire. At any rate, there is a need to immediately solve these problems concerning deterioration.
Consequently, the present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a non-crosslinked flame-retardant resin composition which possesses sufficient flame retardancy, mechanical properties, flexibility and workability, and also possesses excellent heat resistance over a long period of time as it is hard to be molten when used under high temperature environment and not deteriorated even if used in contact with a vinyl chloride resin material and the like.
In addition, another object of the invention is to provide a non-halogenous insulated wire using the above-described non-crosslinked flame-retardant resin composition as an insulated covering material, and a wiring harness including the non-halogenous insulated wire.